Explain Graph Database

A Graph is just data that has a defined structure.E.g. lists, trees, maps, objects are graph data structures. A Graph is the general data structure for storing related data.
The records in a Graph database are called “Nodes” which are connected through “Relationships” that always have a direction. The traditional visual representation uses circles for Nodes and lines for Relationships.The most common example is the relationship between people on a social network such as Facebook.A graph database is a big dense network structure. While it could take an RDBMS hours to sift through a huge linked list of people, a graph database uses sophisticated shortest path algorithms to make data queries more efficient.
Examples includes AllegroGraph,Sones,Neo4j etc.